1. Field of the Invention
A panel clamping assembly of the type for edge gluing wooden boards, doors, frames and the like, and more particularly a panel clamping assembly that uses commercially available bar clamps.
2. Related Art
Lumber panels are used extensively in fine furniture making and cabinetry. Large wood panels are created by gluing smaller boards together edge-to-edge. During this process, adhesive is applied to the mating edges, and then the boards pressed together using clamps. Sometimes, dowel pins, biscuits, or splines are used to help align the boards and improve joint strength. Clamp pressure is maintained until the adhesive has set.
Quality edge glued panels depend on strong glue bonds, closed joints, aligned surfaces and perfectly flat, planar edges. Edge glued boards that twist, cup or rack during the gluing process result in a panel that at best is difficult to work with and at worst unsuitable for the intended application.
Gluing boards into suitable panels can be a stressful operation. Handling long boards can be awkward. Keeping the boards aligned and in place before the glue sets can be difficult. If not careful, misapplied or dripping glue can cause a sticky mess. And limited glue curing time demands swift work.
To achieve high quality finished panels, skilled woodworkers take great care during the laminating process to ensure that freshly glued boards are held flat and undisturbed while the adhesive sets, and that clamping pressures are distributed evenly across the boards. The skilled worker will also assure that the clamps apply pressure centrally through the boards so as to minimize unbalanced and torsional stresses within the wood. Alternating clamps on opposite sides of the panel and evenly spacing the clamps are two techniques used to counterbalance unwanted induced stresses.
Various commercial attempts have been proposed to assure consistently flat edge-glued panels, some aimed at the commercial furniture manufacturing industry, whereas others are suited for the small cabinet shop and home woodworking enthusiast. Perhaps the best known example of a panel laminating system directed to the small cabinet shop is sold under the trade name Plano, marketed by Advanced Machinery Imports Ltd., of Newcastle, Del. The Plano vertical glue press, as it is known, comprises two or more vertically oriented clamps which surround all four sides of a gluing panel. Each clamp includes two opposing vertical rails formed by aluminum extrusions that sandwich the boards. The vertical rails have a generally U-shaped configuration wherein the two legs at the top of the “U” engage the wooden boards directly. Thus, for each vertical rail, two legs of the U make contact with each face of the gluing panels. Upper and lower linking arms join the two vertical rails and support the wooden panel from above and below. A screw mechanism associated with the upper linking arm comprises the sole means by which pressure is applied to the gluing panels in both the horizontal and vertical directions.
While generally effective at producing consistently flat panels, there are numerous disadvantages with the Plano vertical glue press. The system is composed entirely of specially manufactured items which are expensive and beyond the means of many woodworking enthusiasts and small shops. Another disadvantage of the Plano system resides in its committed use to one specific task—edge gluing wooden boards into panels. It is not convertible to other uses and there are no components of the Plano press assembly that can be detached and used for other purposes. Furthermore, horizontal and vertical clamping pressure for each clamp assembly is provided by a single screw associated with the upper linking arm. It is very difficult for this type of arrangement to produce ideal proportions of vertical and horizontal clamping pressure. Horizontally applied pressure, i.e., pressure exerted onto the face of the boards by the U-shaped vertical rails, is a function of the amount of pressure applied by the screw wheel. In other words, horizontal force can only be increased simultaneously with increased vertical force and vice-versa. There is no mechanism by which horizontal force to keep the boards flat can be increased while vertical pressure to squeeze the board edges together remains constant, nor by which different proportions of horizontal and vertical pressure can be applied to the boards. Thus, in situations where proportionally more pressure is required horizontally than vertically, the Plano system cannot accommodate. Yet another shortcoming of the Plano vertical glue press resides in the U-shaped configuration of the vertical rails. Because the rails are relatively wide, they cover relatively large areas of the wood during the clamping operation. When glue squeezes out from the edges during glue-up, the regions of wood covered by the rails, i.e., inside the “U,” are inaccessible and therefore not all of the glue squeezed from the joints can be cleaned before it sets. Also, the wide vertical rails disadvantageously dissipate the horizontal clamping force over a relatively large area. The wide distribution of force is more likely to compel excessive tightening of the clamping screws in order to achieve the needed horizontal clamping forces. Keeping in mind that horizontal clamping pressure increases as a function of vertical pressure, excessively tightened clamping screws can lead to overcompression in the vertical direction, resulting in excessive glue squeeze out from the joints, too much induced stress in the boards, and a weaker finished panel.
Another example of a vertical panel clamping and assembly rack for small production shops can be found in U.S. Pat. No. 5,702,561 to Phillips, issued Dec. 30, 1997. Phillips discloses an apparatus and method for edge gluing wooden boards wherein the boards are supported on a lower spacer bar and stacked against a series of co-planar center support channels. Outer press bars are carried on cantilevered threaded bolts and screwed, with the aid of nuts, against the wooden boards to press them against the center support channels. Conventional bar clamps are then used to provide pressure while the adhesive sets. Numerous disadvantages are evident from the Phillips system. Firstly, the center support channels and press bars have wide flat contact surfaces, resulting in a large surface area of the wooden panels covered during the gluing operation. This frustrates glue clean-up, disadvantageously dissipates clamping force, and can result in staining of the wood, as well as uneven drying of the glued joints. Also, there is no provision for supporting the bar clamps directly from the assembly rack.
Some commercially available systems are suited only for large scale production. These systems employ various techniques to assure consistently flat panels. Examples of commercial grade systems may be found in U.S. Pat. No. 4,547,255 to Yow, issued Oct. 15, 1985, and in U.S. Pat. No. 6,779,576 to Cable, issued Aug. 24, 2004. Both of these systems describe highly automated pieces of capitol equipment for producing consistently flat edge glued panels from wooden boards. Their designs are beyond the reach of all but large-scale production furniture makers and material suppliers. As a result, they do not employ techniques or devices which are common to home woodworkers and small shop environments. Furthermore, they represent single use, dedicated machines whose components are not suitable for alternative uses.
Accordingly, there is a need for an improved panel clamping assembly of the type for edge-gluing wooden boards, doors and frames that is suitable for use in small cabinet shop and home woodworking environments. Furthermore, there is a need for a panel clamping assembly that uses commercially available, conventional bar clamps, that is convenient to use, and which permits the bar clamps to be readily removed from the clamping assembly for use in other applications.